Process for making electrical conductors consisting of vanadium oxide and titanium oxide



Patented Feb. 23, 1943 PROCESS FOR MAKING ELECTRICAL CON- DUCTORS CONSISTING F VANADIUM OXIDE AND TITANIUM OXIDE Eugene Wainer and Norman R. Thielke, Niagara Falls, N. Y., assignors to The Titanium Alloy Manufacturing Com corporation of Maine pany, New York, N. Y., a

No Drawing. Application July 17, 1940, Serial No. 346,058

1 Claim.

This invention relates to new and useful compositions comprising vanadium titanates and methods of making the same.

' In electrical circuits involving the use of high frequency currents, materials which have the combination of electrical properties of low or median resistance, high power factor and fairly high dielectric constant, plus a large negative temperature coefficient (that is, as the temperature increases the dielectric constant and power factor values rapidly increase) would be of con siderable value in such circuits, particularly if available in a chemical form stable over a wide range of temperature, pressure and chemical conditions, and if available in a variety of controlled particle sizes. Such materials would be useful as volume controls for radio circuits where such volume control is determined by uniform variation of a standard resistance, as safety valves in high tension high frequency circuits for limiting voltages, as safety valves in. circuits involving changes in frequency where a limit is desired on the extent of frequency change, and as temperature limiting devices in high frequency and/or high tension circuits.

In accordance with this invention, an entirely new group of compounds has been discovered, which are suitable for the uses listed above. These compounds are those which vary in composition from 2 moles of V205 per mole of T102 to 1 mole of V205 per 31 moles of TiOa, and are identified as vanadium titanates. A number of definite compounds may exist in this series, some of which may have the following formulae: V4'I'i012, VzTiOv, VzTlaOm, Vz'Ii'isOav, VzTisiOcv. On the other hand, certain of the members of this series may exist as mixtures of vanadium titanates of different formulae, or mixtures of certain vanadium titanates with TiO-i or V205. In fact mixtures outside the molecular limits specified above have useful electrical properties.

In general, however, a composition varying from 6% to 82% V205 and 94% to 18% T: is preferred. Each member of this series possesses the required electrical properties, and finds utility in high frequency circuits for the purposes mentioned above. All have relatily low resistance, high power factor, high dielectric constant, high temperature coefficients, and tend to act as enormous reservoirs of high frequency.

power as the temperature rises, in view of the fact that as the temperature increases the power factor and dielectric constant also increase, Since the amount of energy dissipated (in the form of heat) in the above described bodies is proportional to the product of the dielectric constant and power factor, the application of such materials as safety valves in high frequency circuits and as high frequency resistance heaters (in view of their refractoriness) is obvious.

These compounds may be made in a variety of ways. For example, solutions of the oxides in sulphuric acid may be mixed, evaporated to dryness and suitably calcined, or a mixture of hydrates may be prepared by precipitation from a solution of the oxides by the addition of ammonia or organic amines, followed by calcination of the mixed hydrates. However, it is preferred to make these compounds by suitably calcining (in ordinary calcination atmospheres, such as air, which are sufficiently oxidizing in nature to insure that vanadium is kept in the pentavaient state and titanium in the quadrivalent state) an intimate mixture of the finely divided oxides themselves, such as at a temperature in excess of 2000 F. For those compositions of T102 and V205 containing 35 or more percent of V205 a rapid and complete reaction is obtained at HOW to 1800 F.; for those compositions containing 2'5% to 35% V205 a rapid and complete reaction is obtained at 1800 to 1900 F.; while for those compositions containing less than 25% V205 a temperature of at least 2000 F. is preferred for complete combination. Although at the temperatures mentioned a complete reaction is obtained in a short period (30 to 45 minutes) an enhancement of the desirable electrical properties is obtained if the calcination is continued at the specified temperature for at least two hours after the period that previous reactions have shown chemical combination to be complete. The extra roasting period causes a decided increase in size of individual crystals. In each case, a highly crystalline glistening dark brown residue is obtained, in which the microscopical identity of either of the original constituents is lost. It is therefore presumed that a definite chemical combination, or a mixture of combinations, is formed in each case, and that they should be designated as vanadium titanates.

In preparing these compounds directly from the oxides, appropriate mixed together, water is then added, and

The reacted product is then ground to coarse sizes by crushing in rolls. If a finely divided product is desired, the material is milled with a slip 'is discharged and g then calcined for 4 hours water in a ball mill to the desired size, dried and then disintegrated. If a solid body is desired, the milled material may be pressed into the required shape and refired at an elevated temperature.

Examples of specific methods of practicing the invention are as follows:

Exmm 1 Toj'prepare V2Ti1s031, 214 grams of hydrated vanadium pentoxide (equivalent to 181.90 grams of- V20 is mixed with 1280 grams of pigment grade T102. 800 cc. of water is added and the batch is ground in a ball mill for 2 hours. The thoroughly dried, and at 2000 F., cooled and then ground to ---325 mesh. The yield is 1450 grams or approximately theoretical.

EXAMPLE 3 To prepare V2TisO1'l, 214 grams of hydrated vanadium pentoxide (equivalent to 181.90- grams of V205) is mixed with 480 grams of pigment grads TiOz. 450 cc. of water is added and the batch is ground in a ball mill for 2 hours. The slip is discharged, thoroughly dried and calcined for 3 hours at.- 1850 F., cooled, and then ground to -325 mesh. The yield is 658 grams Table 0 owcr Dielectric Temperature 1 factor constant Per cent 16.3 101. 1 17.3 1112.0 18. 5 102. 7 23. 6 1117. 5 28. 1 112.0 32. l 116. 5 lili. 6 121. .4 41.0 1 127. 3 47.15 lav-.1

In addition to the uses mentioned above, some of the vanadium tltanates of the present invention possess properties which indicate possibilities in connection with the rectification of alternating electric currents. Furthermore, they may be utilized, in combination with titanium oxide, to enhance the photosensitive properties of the latter.

As many variations are possible within the scope of this invention, it is not intended to be limited except as defined by the appended claim.

We claim:

The method which comprises calcining a mixture consisting essentially of 6.8 to 82% vanadium pentoxide and 93.2 to 18% titanium dioxide at a temperature in excess of about 1700 F. for a period of time suflicient to insure change of color of the mixture to a black color and under conditions sufiiciently oxidizing to insure that the vanadium is kept in the pentavalent state and the titanium in the quadrivalent state.

- EUGENE WAINER.

NORMAN R. THIELKE. 

